Centrifugal blower



Feb. 2s, 19a? B. ECK 3,306,528

CENTRIFUGAL BLOWER Filed Sept. 22, 1965 3 Sheets-Sheet 1 NVENTR Bruna E @,Q

Feb. 28, 1967 l B. ECK 3,306,528

CENTRIFUGAL BLOWER Filed Sept. 22, 1965 v 5 Sheets-Sheet 2 Smm@ SQL Feb, Z8, 1967 B. ECK 3,306,528

CENTRIFUGAL BLOWER Filed Sept. 22, 1965 5 Sheets-Sheet 5 United States Patent O 3,306,528 CENTRIFUGAL BLOWER Bruno Eck, Geisbergstrasse 24, Cologne-Klettenberg, Germany Filed Sept. 22, 1965, Ser. No. 489,371 19 Claims. (Cl. 230-127) The present application is a continuation in part application of my copending application Serial Number 128,063 filed July 31, 1961, now abandoned.

This invention relates to centrifugal blowers.

The construction of the inlets of the impeller cover plates of centrifugal blowers causes some diiculties. This is particularly the case in the construction of drum impeller blowers since the flow must be deected an angle of 90 over a short distance. In the case of a high intake capacity, axial inlet velocities occur at this point which, in certain cases, are higher than the outer peripheral velocity. Flow separation at this point caused thereby may have very serious consequences on the efliciency and noise production.

Inlet nozzles, reduced in diameter towards the impeller axis of very different types and curved cover plates have been used. Successful results can be obtained by these constructions which, however fail in the case of small constructions or low Reynolds numbers. For known reasons, it is then no longer possible to cause the ilow to adhere in the inlet nozzle and, in addition, it is practically impossible to reduce the size of rotors of the best known construction in geometrical proportions because the blades would then become so small that, on the one hand they would not be resistant to vibrations and, on the other hand they would already be situated in a region in which total laminar flow occurs.

For this reason, it has been necessary to make the diameter ratio between internal diameter and external diameter of the impeller smaller and to reduce the number of blades considerably. Whereas in large construction diameter ratios of about 0.9 and blade numbers of about 60 to 70 are used, it is necessary in small constructions to decrease the diameter ratios to 0.7 and the blade numbers to lO to 12. Due to the necessarily smaller diameter ratio, the intake capacity is reduced, this being all the more disadvantageous since the high intake capacity is one of the considerable advantages of the drum impeller. The consequences of these factors are of considerable importance since the dimensions and construction expenditure become very great and many desirable uses of the blowers are excluded.

In addition to this, the known drum impellers of high intake capacity can be used only at low peripheral speeds due to the very small radial depth of the blades. In contrast thereto, according to the present invention, considerably larger radial blade depths are obtained for the same intake capacity. For this reason, much higher peripheral speeds are possible, so that at higher pressures, for which the known drum impellers were unsuitable, drum impellers according to the invention can be used.

An object of the present invention is to provide a new and improved centrifugal blower.

Another object of the present invention is to provide a new and improved drum impeller blower which overcomes the aforementioned diiliculties.

Yet a further object of the present invention is to provide a new and improved drum impeller for a centrifugal blower of high intake capacity which may be operated at comparatively high peripheral speeds.

Yet a further object of the present invention is the provision of a drum impeller of high intake capacity for a centrifugal blower having larger radial blade depths for a given intake capacity.

Still another object of the present invention is the provision of a drum impeller of high intake capacity for use in a centrifugal blower which is capable of developing higher pressures than has heretofore been feasible with such blowers.

Further objects and advantages of the present invention will become apparent as the following description proceeds. The features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of the specification.

In accordance with these and other objects, the abovementioned deflection difficulties are overcome by means of a fundamentally new solution. These usual 90 deflection of air in the interior of the drum impeller is abandoned altogether, and the deflection is shifted to a part of the impeller blades. For this purpose, the blade end is made at the air-inlet side without the usual cover plate and the free ends of the blades are peripherally bent over so as to produce an axial inlet at this place, these ends thus acting like an element of an axial blade. The curved blades thus have axially-terminating ends at the inlet side.

Over this radial region, after installation, an outer annular cover ring is drawn which separates the inlet side of the blower from the pressures side and also serves to secure the blades.

More specifically, according to the present invention there is provided a centrifugal blower of the drum impeller type having a generally volute housing. The impeller drum is formed of a number of impeller blades and is rotatably mounted within the housing. The impeller drum has an open end axially aligned with the inlet of the housing. In accordance with the present invention, each of the impeller blades has a portion extending radially inwardly of the inlet and a portion extending radially outwardly of the inlet to provide an internal diameter of the drurn less than the diameter of the inlet and an external diameter of the drum greater than the diameter of the inlet, and the portions of the blades adjacent the open end of the drum are of reduced external diameter and bent in a peripheral direction. A cover ring is provided over the reduced diameter portion of the blades to separate the inlet of the blades from the outlet of the housing.

For a better understanding of the present invention, reference may be had to the accompanying drawings,

` wherein:

FIG. 1 is a front elevational sectional view,.somewhat in schematic form, of an axial inlet blower of the prior art with part of the housing and impeller cut away;

FIG. 2 is a sectional side elevational view of FIG. 1 with certain portions of the housing cut away;

FIG. 3 is an enlarged fragmentary view of a portion of FIG. 1 modified to incorporate and illustrate an embodiment of the present invention;

FIG. 4 is a sectional view of the embodiment of FIG. 3 taken along line 4 4 of FIG. 3, and assuming that FIG. 3 shows the complete structure;

FIG. 5 is a sectional view of the embodiment of FIG. 3, taken along the line 5 5 of FIG. 3, and assuming that FIG. 3 shows the complete structure;

FIG. 6 is a sectional View of the embodiment of FIG. 3, taken along line 6-6 of FIG. 3, land assuming that FIG. 3 shows the complete structure;

FIGS. 7, 8, 9, l0 and 11 are fragmentaryectional views somewhat similar to FIG. 3, but showing additional modifications of the present invention;

FIG. 12 is a sectional view of the modication of FIG. l1, taken along line 12-12 of FIG. l1;

FIG. 13 is -a fragmentary sectional view similar to FIG. 3 rbut illustrating another embodiment of the present invention;

FIG. 14 is a fragmentary view in effect comprising a left side view of FIG. 13 and including construction lines illustrating how the particular shapes were arrived at; and

FIGS. and 16 are fragmentary sectional views of still other embodiments of blowers according to the present invention.

Referring now t-o FIGS. 1 and 2, there is shown a centrifugal blower according to the prior art of the best known construction which comprises generally voluteshaped housing I and a drum impeller 2 consisting of a disc 3 and :a curved cover plate 47 between which latter parts forwardly-curved blades S are mounted. The disc 3 is connected to a driving shaft 6 which is driven, for example, -by a belt pulley. The housing 1 is provided with an axial inner converging inlet 7 and a tangential outwardly located outlet 8. It will be seen that the drum impeller 2 has an open end 2a axially aligned with the inlet 7 and that the blades 5 discharge fiuid radially into the outlet 8. The nozzle-shaped inlet 7 and the rounded cover plate 4 as well as the large ratio between the internal diameter and the external diameter of drum 2 with the short radial blades 5 are known.

In accordance with the present invention, there is illustrated in FIGS. 3, 4, 5 and 6 the construction of the present invention whereby the blower of FIG. l, and particularly the -blades of the impeller are modified to eliminate the difficulties set forth above. As there illustrated, there is provided a drum 11 having blades 12, and the forward portion 12a of the blades 12 being bent forwardly peripherally so as to form an inlet angle beta, as shown in FIG. 5. In the cross section parallel to the axis of rotation which is represented by FIG. 5, the blade end portions 12a are forwardly bent in the directions of rotation, while, as shown in FIG. 6, the main portion of each blade has in a plane perpendicularly to the axis, a curved cross section, forwardly curved in FIG. 6 and rearwardly curved in FIG. 12.

A cylindrical cover ring 14 is arranged over an axial inlet. FIGS. 4 and 6 show the subsequent transition to the normal forwardly-curved blades, the inner edges 12b 'of which extend parallel to the drum axis. In spite of the smaller diameter ratio, the construction of the invention shown in FIGS. 4 and 6 has a higher intake capacity than the known construction shown in FIGS. 1 and 2. The parts of the blades which terminate in forwardlycurved blade portions may also be twisted in a known manner. In the developed cylinder section shown in FIG. 5 the transition from Athe peripherally bent inlet blade portions part to the main blade portions can clearly be seen. A cover ring 14 is positioned on the drum 11 over the forwardly bent portions 12a of the blades 12.

In accordance `with the modification shown in FIG. 7, the blades have a bent blade part 26a of reduced external diameter and -a cylindrical cover ring 21 merges with a rounded portion into a radially short cover plate on the main 'blade part.

In the modification of the present invention illustrated in FIG. 8, a cover ring 2S has an outward rounding and due to the drag of the boundary layer in that locality it is sometimes possible to lobtain a sharper deiiection.

In the modiiication of the present invention shown in FIG. 9 a peripherally bent inlet part 2S is separate from the main -blade 29 and the number of inlet lblade parts 28 may be greater or less than the number of the other blades 29. The inlet part 28 is bent forward and peripherally covered by a cover plate 30.

In the modification shown in FIG. l() the outer cover ring 35 inwardly convex and has an inlet portion outwardly extended beyond the outer diameter of the impeller drum 36. The intake capacity of the impeller drum 36 can thus be increased still further.

FIGS. 1l and 12 show another modification of an outer cover ring somewhat similar to the modification of FIG. 7. Specifically, FIGS. l1 and 12 show an impeller with backwardly-curved blades 4t) having a diameter ratio of about `0.5. Unlike the previously described im-pellers, the radial extent of the blades 40 of the present drum is greater than the axial extent.

FIGS. 13 and 14 show how at the air inlet side 45a of blades 45 the blade end is provided with a simple flap 46 which is bent about its chord. In this case it is advantageous to allow the blade to terminate rectilinearly in the region of the bend of the ap, so that a simple, developable-bend is possible as indicated by the line 47. In this blade form, there is a quasi-axial deflection at the inlet, since axial deection is not around a radial edge but around an edge which is inclined to the periphery.

If the bent-over flap 46 has a greater radial extent inwardly, difficulties may arise in regard to questions of strength under consideration of the developing centrifugal forces. For this reason, it is advisable to lweld on short fins 48, FIG. 14 substantially in the streamline direction, so that the blade is given any desired strength. A further reinforcement of the blades 45 may be effected by means of a ring 49 mounted in the region of the bend 0f the blade and consisting, for example, of a tube or a piece of round iron, the inner edge of the -blade being connected to this ring by welding. It may also be advisable to connect the outer edges of the blades by another ring S0 preferably consisting of a fiat iron ring set on edge.

The provision of an inlet nozzle S1, FIG. 13, which with a uniformly rounded portion merges into an -annular cover ring 52, has been found to be important. As will be seen, the diameter of the constricted nozzle part is less than the internal diameter of the cylindrical inlet part of the cover ring 52.

FIG. 15 shows in axial section a centrifugal blower of the drum impeller type, in which the cover ring over the blades 57 is replaced by a cylindrical suction pipe 55 which is connected to the blower housing 56.

FIG. 16 shows a freely-aspirating centrifugal blower of the drum impeller type, in which the bent ends of the blades 60 project from they housing 61.

It will be seen that the present invention provides an entirely new construction of drum impellers which, contrary to the usual construction, aspirates over the full circular area of the impelle-r. With this form of impeller, defiection occurs practically within the front blade part, that is to say, in a zone where, through impulse forces and power supply, defiection losses can be compensated at once, without flow separation. By this step, an outer ring of the air supply is peeled off and introduced directly into the axial part of the blades, while the other part, as heretofore described, is deflected directly into the forwardly-curved blade portions.

If desired, a cylindrical suction pipe is connected to the blower housing and also, in the case of freely aspirating blowers, the desired effect may be obtained by the bent blade part projecting from the blower housing.

In the case of forwardly-curved blades of the drum impeller, the axial inlet may have the same external diameter as the radial impeller part but this step fails, however, when backwardly-curved blades are used. Apparently, this is due to the fact that in this case the edge streamlines, on entry into the backwardly-curved blades, undergo inadequate peripheral deection and hence inadequate increase in pressure, so that excessively different energy absorptions occur. It has been found that nevertheless the invention may also be applied in the caseof backwardly-curved blades if the external diameter of the axial inlet is made smaller. It is then possible to obtain an increase in intake capacity, especially for impellers having a diameter ratio greater than 0.5, and this expedient can also be used advantageously in standard centrifugal blowers, i.e., in blowers of which the blades have a larger radial extension than the axial extension.

It has also been found that, for backwardly-curved blades, it is sufficient to provide the blade ends at the air said housing, peripheral outlet means associated with said` housing, an impeller drum rotatably mounted within said housing, said impeller drum being formed of a plurality of impeller blades, said impeller drum having free edges radially spaced from the axis of rotation to define an open end axially aligned with said inlet means whereby a substantial portion of air entering the open end of said drum enters said blades radially, each of said impeller blades having a portion extending radially inwardly of said inle-t means and a portion extending radially outwardly of said inlet means to provide an internal diameter of said impeller less than the diameter of said inlet means and an external diameter of said impeller greater than the diameter of said inlet means, the portion of the blades adjacent said open end being of reduced exterior diameter and bent in a peripheral direction, and a cover ring over only said reduced diameter portion of said blades and secured thereto to rotate with said blades whereby to separate the inlet to the |blades from said outlet means.

2. A centrifugal blower of the drum impeller type comprising a generally volute housing, axial inlet means associated with said housing, tangential outlet means associated with said housing, a cylindrical impeller drum rotatably mounted within said housing, said impeller drum being formed of a plurality of impeller blades, said impeller drum having free edges radially spaced from the axis of rotation to define an open end axially aligned with said inlet means whereby a substantial portion of air entering the open end of said drum enters said blades radially, each of said impeller blades having a portion extending radially inwardly of said inlet means and a portion extending radially outwardly of said inlet means to provide an internal diameter of said impeller less than the diameter of said inlet means and an external diameter of said impeller greater than the diameter of said inlet means, the portion of the blades adjacent said open end being of reduced exterior diameter and bent in a peripheral direction, and a cove-r ring over only said reduced diameter portion of said blades and secured thereto to rotate with said blades whereby to separate the inlet to the blades from said outlet means.

3. A blower as claimed in claim 2 wherein at said inlet the blades have a projecting flap which is bent over in its chord to form said portion of reduced exterior diameter.

4. A blower as claimed in claim 3 in which the projecting flap is rounded at its inner end so as to produce a semicircular surface.

5. A blower as claimed in claim 3 in which in the region of the bend of the flap the blades extend rectilinearly.

6. A blower as claimed in claim 2 wherein reinforcing fins are welded on to the bent blade portion in the direction of the streamlines.

7. A blower as claimed in claim 2 wherein in the region of the bend of the blades a ring is mounted which comprises a tubular iron member of circular cross section welded to the inner edges of the blades.

8. A blower as claimed in claim 2 wherein a ring of flat iron edge is connected to the outer edges of the blades by welding.

9. A blower as claimed in claim 2 wherein the blades are so designed that the blade angle lies within the range between 38 and 58.

10. A centrifugal blower of the drum impeller type comprising a housing having an inlet side, a drum impeller in said housing formed `of a plurality of blades yand having an axis of rotation, the blades on the inlet side being axially open, said blades having cross sections normal to said axis of rotation which are rearwardly curved, and having in addition thereto at the ends thereof located at said inlet side cross sections parallel to the axis of rotation which are forwardly curved in the direction of rotation so that each blade has a portion at the inlet side which is bent in the peripheral direction, an annular cover 4ring on the exterior periphery of the bent portions of said blades and rotatable therewith, said cover ring having a curved cross section, and an inwardly-narrowed inlet nozzle' mounted directly in front of said impeller and shaped to conform with the curved cross section of said cover ring to deline an inlet to said impeller having uniform rounding, said curved cover ring extending in axial direction at least to the extremities of said bent blade portions.

11. A centrifugal blower as claimed in claim 1 wherein the ratio of the internal diameter of the blades to the external diameter is about 0.9.

12. A centrifugal blower comprising a housing, axial inlet means associated with said housing, tangential outlet means associated with said housing, an impeller drum rotatably mounted within said housing and having an axis of rotation, said impeller drum being formed of a plurality of impeller blades, said blades having free edges spaced from the axis of rotation of said drum to define a drum with an open end axially aligned with said inlet means, the portions of the blades adjacent said open end having cross sections parallel to said axis of rotation which are forwardly curved in the direction of rotation and being bent in a peripheral direction, and a cover ring over said bent portion of said blades and secured thereto to separate the inlet to said blades from said outlet means, said cover ring extending in axial direction to the extremities of said bent peripheral portions.

13. A centrifugal blower comprising a housing, axial inlet means associated with said housing, tangential outlet means associated with said housing, an impeller drum rotatably mounted within said housing, said impeller drum being formed of a plurality of impeller blades, said blades having free edges spaced from the axis of rotation of said drum to dene a drum with an open end axially aligned with said inlet means, the portions of the blades adjacent said open end being bent in a peripheral direction, and a cover ring over said bent portion of said blades and secured thereto to separate the inlet to said blades from said outlet means, the portions of said blades adjacent said open end being of reduced exterior diameter, and said cover ring being disposed over said reduced diameter portion of said blades and secured thereto to rotate with said blades thereby to separate the inlet to the blades from said outlet means.

14. A centrifugal blower of the drum impeller type comprising a generally volute housing, axial inlet means associated with said housing, tangential outlet means associated with said housing, a cylindrical impeller drum rotatably mounted within said housing, said impeller drum being formed of a plurality of axially extending impeller blades defining continuous concave pressure faces, said impeller blades having free edges radially spaced from the axis of rotation to define an open end axially aligned with said inlet means whereby a substantial portion of air entering the open end of said drum' enters said blades radially, each of said impeller blades having a first portion extending radially inwardly of said inlet means and a second portion extending radially outwardly of said inlet means to provide an internal diameter ofsaid impeller drum less than the diameter of said inlet means and an external diameter of said impeller drum greater than the diameter of said inlet means, said rst and second portions of said blades being of substantially equal radial extent, the ends of said blades adjacent said open end being of reduced exterior diameter and bent in the direction of rotation of said drum substantially normal to the axis of said drum to form pumping inlet surface edges, a cover ring over only said reduced diameter portions of said blades and .secured thereto to rotate with said blades whereby to separate the inlet to the blades from said outlet means, and a converging diverging intake nozzle forming said intake means supported by said housing and including a portion extending within said cover ring, said intake nozzle and said cover ring substantially merging adjacent the bent ends of said blades.

15. A centrifugal blower comprising a housing including an outlet means and an inlet nozzle having an annular edge portion; and an impeller drum having an axis of rotation, and including a support at one axial end thereof, a plurality of impeller blades secured to said support projecting in axial direction therefrom, each impeller blade having a free end portion having parallel to said axis a cross section forwardly curved in the direction of rotation so that the end portion is bent in peripheral direction, and a cover ring secured to said free end portions and enveloping the extremities of said end portions so that the same do not project in axial direction from said cover ring, said cover ring having an annular edge portion forming the other axial yend of said impeller drum and surrounding and overlapping said annular edge portion of said nozzle to guide a iluid medium to said blades and to separate said inlet nozzle from said outlet means of said housing.

16. A centrifugal blower according to claim 15 wherein said cover ring is curved in axial planes, so that the diameter thereof decreases toward said annular edge portion thereof.

17. A centrifugal blower accordingto claim 16 where` 'nular edge portion of said cover ring projects in axial direction beyond said extremities of said blades.

References Cited by the Examiner UNITED STATES PATENTS 662,397 11/ 1900 Davidson 230-127 1,161,926 11/1915 Criqui 230134.45 2,160,666 5/ 1939 McMahan 230-127 2,316,608 4/ 1943 McMahan 230-127 2,727,680 12/ 1955 Madison et al. 230--133 3,147,541 9/1964 Hathaway 230-134 FOREIGN PATENTS 487,976 5/ 1918 France. 269,616 1/ 1914 Germany.

DONLEY I. STOCKING, Primary Examiner. 

1. A CENTRIFUGAL BLOWER OF THE DRUM IMPELLER TYPE COMPRISING A HOUSING, AXIAL INLET MEANS ASSOCIATED WITH SAID HOUSING, PERIPHERAL OUTLET MEANS ASSOCIATED WITH SAID HOUSING, AN IMPELLER DRUM ROTATABLY MOUNTED WITHIN SAID HOUSING, SAID IMPELLER DRUM BEING FORMED OF A PLURALITY OF IMPELLER BLADES, SAID IMPELLER DRUM HAVING FREE EDGES RADIALLY SPACED FROM THE AXIS OF ROTATION TO DEFINE AN OPEN END AXIALLY ALIGNED WITH SAID INLET MEANS WHEREBY A SUBSTANTIAL PORTION OF AIR ENTERING THE OPEN END OF SAID DRUM ENTERS SAID BLADES RADIALLY, EACH OF SAID IMPELLER BLADES HAVING A PORTION EXTENDING RADIALLY INWARDLY OF SAID INLET MEANS AND A PORTION EXTENDING RADIALLY OUTWARDLY OF SAID INLET MEANS TO PROVIDE AN INTERNAL DIAMETER OF SAID IMPELLER LESS THAN THE DIAMETER OF SAID INLET MEANS AND AN EXTERNAL DIAMETER OF SAID IMPELLER GREATER THAN THE DIAMETER OF SAID INLET MEANS, THE PORTION OF THE BLADES ADJACENT SAID OPEN END BEING OF REDUCED EXTERIOR DIAMETER AND BENT IN A PERIPHERAL DIRECTION, AND A COVER RING OVER ONLY SAID REDUCED DIAMETER PORTION OF SAID BLADES AND SECURED THERETO TO ROTATE WITH SAID BLADES WHEREBY TO SEPARATE THE INLET TO THE BLADES FROM SAID OUTLET MEANS. 